Method of determining electrode length and bath level in an electric arc furnace

ABSTRACT

A method for the continuous determination of the distance between an electrode tip and level of a bath in an electric arc furnace so as to be able to exactly determine electric energy consumption per tonne of scrap actually melted, electrode wear and the residual liquid bath present in the electric arc furnace after tapping.

CROSS REFERENCE TO RELATED APPLICATION

This application is a 371 application of International PatentApplication No. PCT/DE99/01669 filed May 31, 1999.

FIELD OF THE INVENTION

The present invention relates to a method for continuously determiningthe distance between a tip of an electrode and a steel bath level in anelectric arc furnace.

BACKGROUND OF THE INVENTION

Currently, in electric arc furnaces, the level of the electrode tip at aparticular time during the melting process is not known with sufficientaccuracy. Moreover, the level of the steel bath at the end of a meltingprocess is also not known with sufficient accuracy.

Among other things, the inability to know the level of the electrode tipand the level of the steel bath results from the fact that theelectrodes having varying lengths, there are different clamping heightsof the electrodes and different electrode consumptions.

OBJECT AND SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method withwhich the above-described disadvantages can be largely minimized.

This objective is accomplished by carrying out two special lengthmeasurements and subsequently evaluating the results for the purpose ofcontinuously determining the distance between a tip of the electrode anda level of the bath of the preceding melt in the electric arc furnace.

More specifically, in a method in accordance with the invention, alength measuring system capable of providing a length measurement whichcorrelates to a height of the electrode in the furnace is provided alongwith an optical measuring system capable of generating a horizontal beampath which is arranged at a predetermined vertical distance from areference point. A first length measurement of the electrode isperformed at the end of each melt conducted in the electric arc furnaceby moving the electrode toward the steel bath until a predeterminedstopping criterion of the electrode tip is reached and then determiningand storing a first value of the length measuring system. A secondlength measurement is performed by moving the electrode in a directionaway from the steel bath until the electrode tip interrupts thehorizontal beam path generated by the optical measuring system and thendetermining and storing a second value of the length measuring system.The distance between the electrode tip and the level of the steel bathcan be determined from the first and second values.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an electric arc furnace in which themethod in accordance with the invention is applied; and

FIG. 2 is a schematic view showing the optical measuring system used ina method in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the method in accordance with the invention is usedin conjunction with a furnace vessel 4 which is operatively covered by afurnace lid 3 and includes a refractory lining 7. A steel bath 6 isformed inside the vessel 4 at the bottom and slag 5 covers the steelbath 6. The level of the bath 6 is designated 10, i.e., the height ofthe steel bath 6 from a bottom of the interior of the vessel 4(reference point 14) to the upper surface of the steel bath 6.

Outside of the vessel 4, there is an electrode-lifting cylinder 8connected to an electrode arm 2 which extends over the vessel 4. Anelectrode 1 is connected to the electrode arm 2 and enters into theinterior of the vessel 4. The electrode 1 has an electrode tip 12. Alength measuring system or electrode lift 11 is associated with theelectrode-lifting cylinder 8 and the height (h₁ and h₂) of the lengthmeasuring system 11 is used to determine the length of the electrode 1as described below.

Referring now to FIG. 2, an optical measuring system 9 is also providedand generates a beam path 13. The distance between the reference point14 and the beam path 13 provides a variable a₁ which is used todetermine the length of the electrode 1 as discussed below.

In a method in accordance with the invention, a first measurement ismade towards the end of each melt. The electrode tip 12 is moved in thedirection of the steel bath 6 by suitably varying the control variablesfor the furnace voltage and current. When a specified stopping criterionis reached, the electrode-lifting cylinder 8 is in the position shown inFIG. 1 and the actual value h₁ of the length measuring system, electrodelift 11, is stored and the measuring process is terminated. The stoppingcriterion is defined by a signal behavior of the control variables forfurnace voltage and furnace current, which occurs identically for eachmeasurement. Accordingly, the distance between the electrode tip 12 andthe level 10 of the steel bath 6 is approximately constant for eachmeasurement.

A second measurement is made with the furnace lid 3 swung out to exposethe interior of the vessel 4, as shown in FIG. 2. By means of a suitableautomated system the electrode tip 12 is moved to a known, fixeddistance from the reference point 14. This fixed distance is defined bythe horizontal beam path 13 of the optical measuring system 9, such as apyrometer. As soon as the electrode tip 12 has interrupted the beam path13 of the optical measuring system 9, the electrode 1 is raised. Whenthe beam path 13 no longer is interrupted, the actual value (h₂) of thelength measuring system, the electrode lift 11, is stored.

The bath level 10 is calculated using the equation:

bath level=a ₁−(h ₂ −h ₁).

The distance between the electrode tip 12 and the bath level 10 of thepreceding melt is calculated using the equation:

distance=a ₁−(h ₂−actual value of length measuring systems)−bathlevel+correction for electron consumption between 2 measurements.

Accordingly, it is possible to determine the electrode consumption incentimeters per molten scrap content of a basket and the level of thesteel bath 6 at the end of a melt.

The proposed method is suitable for all electric arc furnaces,especially for d.c. electric arc furnaces.

For carrying out the first measurement, when the proposed method is usedwith a three-phase electric arc furnace, an electrode 1 must be immersedin the steel bath 6 and the described measurement must be carried outwith a second electrode.

Under the condition that the tapping weight can be determinedaccurately, the method developed enables the technologicalcharacteristics, related to the respective melt, in a sump furnace to bestated accurately.

Accordingly, the following, for example, can be stated concerning therespective melt:

consumption of electric energy per ton of scrap actually melted:

residual amount in the furnace after tapping: and

exact consumption of electrode.

The above information and knowledge of the height, at which theelectrode tip 12 is in the furnace at any time, makes it possible toanalyze, optimize, automate and control the process extensively. Some ofthe optimizations and automations that become possible are listed below:

optimizing and automating the melting phases;

optimizing and automating the overheating phase and the field strength;

optimizing the sump amount with the aim of minimizing the energyconsumption and maximizing the output;

minimizing consumption of the refractory materials; and

minimizing the proportion of entrained slag during tapping to improvethe metallurgical work during the pan handling, especially thedesulfurization.

What is claimed is:
 1. A method for continuously determining thedistance between a tip of an electrode and a level of a steel bath in anelectric arc furnace, comprising the steps of: providing a lengthmeasuring system capable of providing a length measurement whichcorrelates to a height of the electrode in the furnace; arranging anoptical measuring system capable of generating a horizontal beam path ata predetermined vertical distance from a reference point; performing afirst length measurement of the electrode at the end of each meltconducted in the electric arc furnace by moving the electrode toward thesteel bath until a predetermined stopping criterion of the electrode tipis reached and then determining and storing a first value of the lengthmeasuring system, and performing a second length measurement by movingthe electrode in a direction away from the steel bath until theelectrode tip interrupts the horizontal beam path generated by theoptical measuring system and then determining and storing a second valueof the length measuring system, the distance between the electrode tipand the level of the steel bath being determinable from the first andsecond values.
 2. The method of claim 1, wherein the furnace is athree-phase electric arc furnace, further comprising the step ofimmersing an additional electrode in the steel bath at the time of thefirst measurement.
 3. The method of claim 1, wherein the electrode ismoved toward the steel bath during the first length measurement byvarying control variables for voltage and current of the furnace.
 4. Themethod of claim 3, further comprising the step of defining the stoppingcriterion of the electrode tip based on the control variables for thevoltage and current of the furnace.
 5. The method of claim 4, whereinthe stopping criterion is defined such that the distance between theelectrode tip and the level of the steel bath is substantially constantfor each measurement.
 6. The method of claim 1, further comprising thesteps of providing the furnace with a lid covering a vessel and swingingthe lid out from a position above the vessel when performing the secondlength measurement.
 7. The method of claim 1, wherein the opticalmeasuring system is a pyrometer.
 8. The method of claim 1, furthercomprising the step of determining the level of the steel bath bysubtracting a difference between the second and first values from thedistance between the optical measuring system and the reference point.9. The method of claim 8, wherein the distance between the electrode tipand the level of the steel bath is determined by subtracting thedetermined level of the steel bath and a difference between the secondvalue and an operative value of the length measuring system from thedistance between the optical measuring system and the reference pointand further adding a correction factor for electron consumption betweentwo successive measurements.
 10. The method of claim 1, wherein thefurnace is a DC electric arc furnace.
 11. The method of claim 1, furthercomprising the step of coupling the electrode to an electrode armconnected to an electrode-lifting cylinder associated with the lengthmeasuring system.
 12. A method for continuously determining the distancebetween a tip of an electrode and a level of a steel bath in an electricarc furnace, comprising the steps of: providing an electrode-liftingcylinder movable relative to a first reference point to move theelectrode relative to the steel bath; arranging an optical measuringsystem capable of generating a horizontal beam path at a predeterminedvertical distance from a second reference point; performing a firstlength measurement of the electrode at the end of each melt conducted inthe electric arc furnace by moving the electrode toward the steel bathuntil a predetermined stopping criterion of the electrode tip is reachedand then determining and storing a first value representative of adistance the electrode has been lifted by the electrode-lifting cylinderrelative to the first reference point, and performing a second lengthmeasurement by moving the electrode in a direction away from the steelbath until the electrode tip interrupts the horizontal beam pathgenerated by the optical measuring system and then determining andstoring a second value representative of a distance the electrode hasbeen lifted by the electrode-lifting cylinder relative to the firstreference point, the distance between the electrode tip and the level ofthe steel bath being determinable from the first and second values. 13.The method of claim 12, wherein the furnace is a three-phase electricarc furnace, further comprising the step of immersing an additionalelectrode in the steel bath at the time of the first measurement. 14.The method of claim 12, wherein the electrode is moved toward the steelbath during the first length measurement by varying control variablesfor voltage and current of the furnace.
 15. The method of claim 14,further comprising the step of defining the stopping criterion of theelectrode tip based on the control variables for the voltage and currentof the furnace.
 16. The method of claim 15, wherein the stoppingcriterion is defined such that the distance between the electrode tipand the level of the steel bath is substantially constant for eachmeasurement.
 17. The method of claim 12, further comprising the steps ofproviding the furnace with a lid covering a vessel and swinging the lidout from a position above the vessel when performing the second lengthmeasurement.
 18. The method of claim 12, further comprising the step ofdetermining the level of the steel bath by subtracting a differencebetween the second and first values from the distance between theoptical measuring system and the second reference point.
 19. The methodof claim 17, wherein the distance between the electrode tip and thelevel of the steel bath is determined by subtracting the determinedlevel of the steel bath and a difference between the second value and anactual value representative of a distance the electrode is operativelymoved by the electrode-lifting cylinder relative to the first referencepoint from the distance between the optical measuring system and thesecond reference point and further adding a correction factor forelectron consumption between two successive measurements.
 20. The methodof claim 12, further comprising the step of coupling the electrode to anelectrode arm connected to the electrode-lifting cylinder.